Do not underestimate the value of inorganic phosphate!

A reduction of phosphorus (P) levels in feed increases the importance of having sure and sufficiently high digestibility coefficients of P. Phytase is, therefore, generally used in feed. However, high digestible mineral P sources are still important for the delivery of sufficient levels of digestible P to the animal.

An adequate phosphorus supply is needed for health and optimal growth. P has an important function in a large number of biological processes. A few of its numerous functions: it’s necessary for bone (and teeth) growth, it is a key element in energy metabolism, plays a role in acid-base buffering in blood, and is a component of tissue cell walls.

In plant materials, about 65% of the phosphate is present in the form of phytate. Monogastric animals lack the enzyme necessary to degrade the phytate, resulting in a low P-digestibility of feed ingredients of plant origin. Addition of highly digestible inorganic phosphates to the diets is needed to fulfil the animal’s P requirement. High total P levels in the diets, result in high P excretion in the manure, leading to environmental pollution. To increase P digestibility in feed and reduce P excretion in the manure, phytases were developed. Phytase addition to the diet leads to an increased digestibility of phytate-P. Due to the anti-nutritional properties of phytate, mainly complexing with protein and free amino acids, degradation of phytate also improves protein digestibility. Therefore, matrix values of phytases are used to predict the total effects of phytase addition on nutrient digestibility and thus performance of animals.

Makkink (2011) described a Dutch experiment in which two phytases were compared. Phyzyme XP, which is an E-Coli 6-phytase produced by a yeast, was compared with a competitor phytase and monocalciumphosphate as a positive control. Feed intake, weight gain and feed conversion were registered and at the end of the experiment, tibia-P concentration was determined. Addition of Phyzyme XP increased gain and tibia-P more than the competitor enzyme at the same dose levels. Partly based on this, higher matrix values of Phyzyme XP were proposed by the producer.

Comparing the results of the Phyzyme XP at the dose levels of 250, 500, 750 and 1000 FTU/kg added to the basal diet (corresponding with 0.49, 0.98, 1.47 and 1.96 g digestible P) with extra

monocalciumphosphate (MCP) added to the basal diet at dose levels of 0.5, 1.1 and 1.8 g P (corresponding with 0.43, 0.94 and 1.53 g digestible P), showed that at the same digestible P levels, MCP resulted in higher gains and higher tibia-P levels than the enzyme addition (see graphs).

This shows that matrix values of phytases may be overestimated and that the use of higher levels of highly digestible monocalcium phosphate may result in better performance of animals.

To compare two commercial phytases relative to the use of monocalcium phosphate, an experiment with broilers was performed[1]. The experiment was performed with three groups of broilers, each group consisting of 12 cages with 6 birds each. The birds were fed one of three experimental diets (table 1): a group receiving a diet with Q-MCP; a group receiving a diet with Q-MCP partly replaced by Natuphos; and a group receiving a diet with Q-MCP partly replaced by Phyzyme. All groups were fed a starter diet for two weeks (weeks 1-2) and a grower/finisher diet for three weeks (weeks 3-5). The matrix values of the tested products are given in table 2.

The use of monocalcium phosphate (Q-MCP) was compared with partial replacement by Natuphos or Phyzyme. For both enzymes matrix values supplied by the manufacturer were used to optimise diet composition.

Table 1: Composition (%) of the starter diets and the grower/finisher diets.

Table 3: Performance of the broilers fed the different experimental diets.

Q-MCP

Natuphos

Phyzyme

SEM

Body weight day 36

2249a

2204ab

2185b

28.6

Week 2-5

Daily gain (g)

72.6a

71.1ab

70.3b

0.5

Feed intake (g/d)

116.8

115.1

114.4

0.8

Feed conversion

1.615

1.623

1.628

0.010

ab: Means in the same row with a different superscript indicates that there is a trend (P<0.10)

Results showed that weight gain was better for the Q-MCP group than for the Phyzyme group. The Natuphos group was intermediate. The differences were caused by slightly higher feed intakes, resulting in similar feed conversion ratios.

Practical least cost formulations show apparently that phytase is an economical source of digestible P. With the current prices of feed-ingredients formulators can be tempted to use high amounts of phytase as digestible P source. However, the risk of overestimating phytase potency is always present.

This experiment was set up to investigate the risks at low digestible P levels. In this experiment, feeds with recommended amounts corresponding with 0.8 g digestible P of two different phytases were compared with a feed without phytase; the feed without phytase contained consequently more MCP. Results show that animal performance on feeds with inclusion of phytase is lower than on a feed solely based on MCP.

These results underline the role of highly digestible mineral phosphorus sources like MCP in safe guarding sufficiently high digestible P levels in high phytase formulations and warn feed formulators for overestimating phytase potency.